CN108689819B

CN108689819B - Novel method for degrading wood chips through catalytic oxidation of polyoxometallate

Info

Publication number: CN108689819B
Application number: CN201810509988.2A
Authority: CN
Inventors: 师楠; 刘�东; 温福山; 陈清泰; 李敏; 殷长龙; 陈坤; 黄强; 娄斌; 于冉; 龚鑫; 张智琛; 蒋瑞雪
Original assignee: China University of Petroleum East China
Current assignee: China University of Petroleum East China
Priority date: 2018-05-24
Filing date: 2018-05-24
Publication date: 2021-03-30
Anticipated expiration: 2038-05-24
Also published as: CN108689819A

Abstract

本发明提供了一种新型多金属氧酸盐复合催化剂催化氧化降解木屑的方法，所述方法包括将木屑、催化剂、溶剂共混，在氧气氛围、一定压力和温度下催化氧化降解木屑，得到氧化产物。所述催化剂为含两种活性中心的双多金属氧酸盐/水滑石复合催化剂，一种催化活性中心选自Keggin型多金属氧酸盐磷钨酸、硅钨酸、磷钼酸、硅钼酸中的一种或多种，另一种催化活性中心选自Dawson型、缺角Dawson型和杂原子取代的Dawson型多金属氧酸盐中的一种或多种；所述反应产物包括芳香族醛、酮类化合物。与现有技术相比，本发明所涉及一种新型的双多金属氧酸盐/水滑石复合催化剂，高效催化氧化降解木屑生成芳香族醛、酮类化合物；本发明选择醇类等有机溶剂为反应介质，通过离心直接将木屑、催化剂与小分子化合物分离，避免萃取过程；条件温和，操作简单，催化剂廉价易得。The invention provides a method for catalytic oxidation and degradation of wood chips with a novel polyoxometalate composite catalyst. The method comprises the steps of blending wood chips, a catalyst and a solvent, and catalyzing and oxidizing and degrading wood chips under an oxygen atmosphere, a certain pressure and temperature, to obtain oxidized wood chips. product. The catalyst is a double-polyoxometalate/hydrotalcite composite catalyst containing two active centers, and one catalytic active center is selected from Keggin-type polyoxometalate phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, and silico-molybdenum. One or more of the acid, the other catalytic active center is selected from one or more of Dawson type, missing corner Dawson type and heteroatom substituted Dawson type polyoxometalates; the reaction product includes aromatic aldehydes and ketones. Compared with the prior art, the present invention relates to a new type of double polyoxometalate/hydrotalcite composite catalyst, which can efficiently catalyze oxidation and degrade wood chips to generate aromatic aldehydes and ketone compounds; the present invention selects organic solvents such as alcohols as The reaction medium directly separates wood chips, catalysts and small molecular compounds by centrifugation, avoiding the extraction process; the conditions are mild, the operation is simple, and the catalyst is cheap and easy to obtain.

Description

Novel method for degrading wood chips through catalytic oxidation of polyoxometallate

Technical Field

The invention relates to a method for degrading wood chips by catalytic oxidation of a novel polyoxometallate composite catalyst, belonging to the technical field of biomass energy sources.

Background

Fossil resources such as coal and petroleum are always main sources of fuels and chemical raw materials, however, with the increasing exhaustion of traditional resources and the increasingly prominent environmental problems, the search for green, environment-friendly and sustainable substitutes for fossil resources becomes particularly urgent. Biomass refers to any organic substance that can grow through photosynthesis using the atmosphere, water, land, and the like. In a narrow sense, biomass comprises straws, trees, wastes of agricultural processing and the like except grains, fruits and seeds, and is a green and widely distributed renewable resource.

The wood chip is an important biomass resource, widely exists in the plant world, and is also one of important industrial wastes in the industries of agriculture, building, paper making and the like. The main components of the wood chip are cellulose, hemicellulose and lignin, wherein the cellulose is polysaccharide formed by connecting glucose through 1, 4-beta-glycosidic bonds, the hemicellulose is a heteromultimer formed by connecting different types of monosaccharides such as xylose, the lignin is a three-dimensional network polymer formed by connecting three aromatic precursors taking phenyl propane as structural elements through C-C bonds and C-O-C bonds, and the lignin is the only natural aromatic high molecule which exists in large quantity in the nature. Through degradation and conversion, the wood chips can be used for producing fuels and organic industrial raw materials, and are a potential petroleum substitute. Under the oxidizing atmosphere, the wood chips can be degraded into aldehyde, ketone, quinone, acid, ester and other compounds with high added value and polyfunctional groups, so that high-value utilization of the wood chips is realized. Therefore, the new biomass material and product based on the wood chips are vigorously developed, so that the dependence of China on fossil resources is relieved, the national resource and energy safety is guaranteed, and the pollution of the developed fossil resources to the environment is relieved.

The key point of wood chip oxidative degradation lies in the oxidative degradation of lignin, but due to the complex chemical composition and good chemical stability of lignin, the degradation cost is high, so that the efficient conversion and utilization of the lignin face huge challenges. At present, oxygen, hydrogen peroxide and the like are commonly used as oxidants to degrade wood chips, and catalysts are usually added to accelerate the reaction rate and control the reaction process. Common catalysts mainly include enzymes represented by laccase and the like, biomimetic catalysts represented by porphyrin and the like, metal organic catalysts represented by methyltrioxorhenium, Co (Salen) and the like, mesoporous catalysts represented by molecular sieves and polyoxometallate catalysts represented by Keggin type polyoxometallate. Among many catalysts, the polyoxometallate catalyst is favored in degrading wood chips due to its variable and adjustable structure, good stability, reversible redox, and high catalytic efficiency and selectivity.

For example, chinese patent CN106755011A discloses a method for catalyzing hydrolysis of lignocellulose with polyoxometallate, which uses Keggin type polyoxometallate containing different heteroatoms as a catalyst or a composite catalyst to catalyze hydrogenation of lignocellulose for hydrolysis and prepare monosaccharide therefrom, wherein the reaction conditions are mild, but the post-treatment is relatively complex, and the recycling effect of the method needs to be improved. The invention patent CN107098803A discloses a method for separating, purifying and degrading lignin, which prepares lignin with high purity and complete structure through multiple times of crushing and enzymolysis, and efficiently degrades the lignin by a Keggin type polyoxometallate-Raney nickel series catalyst to obtain an aromatic platform compound. However, polyoxometallate catalysts for catalytically oxidizing and degrading wood chips are all concentrated in a Keggin structure and a water system, so that the reaction selectivity is low, the catalyst is difficult to separate, and the catalytic degradation efficiency of lignin in the wood chips is further improved. Therefore, there is a need to develop a new catalytic oxidative degradation wood chip system.

Disclosure of Invention

The invention provides a method for degrading wood chips by catalytic oxidation of a double polyoxometallate/hydrotalcite composite catalyst, which comprises the following steps:

mixing wood chips, a catalyst and a reaction solvent, introducing an oxidant into a high-pressure reaction kettle for oxidative degradation to obtain an oxidation product, and collecting the oxidative degradation product through centrifugal separation; the oxidation product comprises small molecular compounds such as aromatic aldehyde and ketone;

the catalyst is a double polyoxometallate/hydrotalcite composite catalyst and comprises two catalytic centers, wherein both the two catalytic centers are polyoxometallates, and the carrier is hydrotalcite and forms an intercalation compound with two active centers;

the oxidant is oxygen;

the reaction solvent is alcohol or alcohol-containing mixed solvent;

preferably, the wood chips are selected from one or more of southern yellow pine, willow, miscellaneous tree, straw, reed grass, sodium lignosulfonate and calcium lignosulfonate;

preferably, one catalytic active center in the catalyst is selected from one or more of Keggin type polyoxometallate phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdic acid, and the other catalytic active center in the catalyst is selected from Dawson type polyoxometallate P₂W₁₈Unfilled corner Dawson type P₂W₁₇Heteroatom-substituted Dawson type P₂W₁₇Mo、P₂W₁₅Mo₃、 P₂W₁₃Mo₅、P₂W₁₇V、P₂W₁₅V₃、P₂W₁₃V₅、P₂W₁₅Mo₂V、P₂W₁₅MoV₂One or more of;

preferably, the carrier is magnesium aluminum hydrotalcite [ Mg ]₆Al₂(OH)₁₆](CO₃)。

Preferably, the mass fraction of one catalytic activity center in the catalyst is 2-10%, and the mass fraction of the other catalytic activity center in the catalyst is 5-20%;

preferably, the temperature of the oxidative degradation reaction is 100-180 ℃, and the reaction time is 2-10 h;

preferably, the oxidizing agent O of the oxidative degradation reaction₂The initial pressure of the pressure regulator is 0.2-2.5 MPa;

preferably, the concentration of the catalyst in the solution is 0.05 g/ml;

preferably, the ratio of the wood chips to the reaction solvent is 500 mg: 20ml of the solution;

preferably, the reaction magnetic stirring speed is 500-1500 r/min;

preferably, the reaction solvent is one or more of alcohols such as methanol and ethanol and alcohol-containing mixed organic solvents;

the invention provides a novel method for degrading wood chips by catalytic oxidation of double polyoxometallate/hydrotalcite, which mainly comprises the following steps: mixing wood chips, a catalyst and a reaction solvent, introducing oxygen into a high-pressure reaction kettle, carrying out oxidative degradation reaction, and carrying out centrifugal separation to obtain an oxidation product; the product comprises aromatic aldehyde and ketone compounds; the catalyst is a double polyoxometallate supported catalyst, one polyoxometallate is selected from one or more of Keggin type phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdic acid, the other polyoxometallate is selected from one or more of Dawson type, unfilled-angle Dawson type and heteroatom-substituted Dawson type polyoxometallate, and the polyoxometallate is inserted between hydrotalcite layers to form a polyoxometallate-substituted intercalation structure; the reaction solvent is alcohol or alcohol-containing mixed organic solvent. Compared with the prior art, the two polyoxometallates are selected as double catalytic active centers and form an intercalation compound with hydrotalcite, so that the activity of the catalyst can be adjusted highly flexibly, and the sawdust can be oxidized and degraded efficiently and selectively to generate aromatic aldehyde and ketone compounds; according to the invention, organic solvents such as alcohols are selected, so that the product can be prevented from being condensed again, sawdust, catalyst and small molecular compound can be directly separated through centrifugation, and the extraction process is avoided; the method has mild conditions and simple operation.

Detailed Description

In order to make the technical scheme of catalytic oxidation degradation of wood chips by polyoxometallate more clear and complete, the method is further described below by combining specific implementation cases. The described embodiments are only some of the embodiments of the invention, not all of them.

The invention has no special limitation on the source and purity of the non-gas raw material, and the raw material is available on the market, and is preferably analytically pure except the wood chips; the oxygen source and purity are not particularly limited and may be commercially available, and the purity is preferably 99.9%.

The reaction vessel is a Ha's high-pressure reaction kettle.

The reaction qualitative and quantitative detection instrument is a gas chromatography-mass spectrometry (GC-MS) instrument, Agilent (7890A-5975C), the mass spectrometry ion source is an EI source, and the gas chromatography column is an HP-5MS 30mx0.25mmx0.25um capillary column.

The method for preparing the polyoxometallate is not particularly limited in the present invention, and is a method well known to those skilled in the art.

Example 1

Preparing Keggin type polyoxometallate: taking silicotungstic acid as an example, 198g of sodium tungstate is dissolved in 250ml of water at 50 ℃, 240ml of 3M HCl is added, 100ml of aqueous solution containing 11g of sodium silicate is added under vigorous stirring, the pH value is adjusted to 1 by HCl, the solution is concentrated to 400ml at 80 ℃, then the solution is adjusted to pH value of 2 by KOH, a large amount of KCl is added, filtration is carried out, and a filter cake is dried and recrystallized to obtain the silicotungstic acid catalyst. Phosphomolybdic acid, silicomolybdic acid, phosphotungstic acid were obtained by the same method.

Example 2

Dawson type polyoxometallate P₂W₁₈The preparation of (1): 62.5g of tungstic acidMixing sodium and 52.5ml phosphoric acid, refluxing for 1 hour, gradually dropwise adding hydrogen peroxide into the mixed solution, reacting for 0.5 hour, cooling to room temperature, adding 25g NH₄Cl, filtration, dissolution of the filter cake in 150ml of water, addition of 25g of KCl, standing overnight, filtration on a Buchner funnel and washing three times with water, and recrystallization of the solid under water at 65 ℃ to give polyoxometallate P2W18 of Dawson type.

Example 3

Unfilled Dawson type polyoxometallate P₂W₁₇The preparation of (1): 40g P₂W₁₈Dissolving in water, and adding dropwise 10g KHCO₃The mixture is vigorously stirred for 2 hours at room temperature, filtered, and a filter cake is recrystallized twice in hot water to obtain the unfilled Dawson type heteropoly acid P₂W₁₇。

Example 4

Preparation of substituted polyoxometallates of Dawson type with a number of W atoms less than 3: with P₂W₁₇V is 20g P₂W₁₇Dissolved in 112ml of 0.5mol/L HCl solution and designated as solution A. 0.5g of NaVO₃Dissolved in 8ml of water and designated solution B. The solution B was added dropwise to the solution A with vigorous stirring, followed by the addition of 17.5g of KCl. Filtering, recrystallizing the filter cake in 0.5mol/L HCl solution at 50 ℃ to obtain P₂W₁₇V。P₂W₁₇Preparation method of Mo and P₂W₁₇V is the same, and the Mo source used is Na₂MoO₄。

Example 5

Preparation of a polyoxometalate of Dawson type in which the W atom is substituted by a heteroatom and the number of substitutions is greater than 3: with P₂W₁₅Mo₃For example, 20g of Na₂P₂W₁₅O₅₆Adding into a reactor containing 3.3g of Na₂MoO₄To 0.5mol/L HCl solution, after complete dissolution, 25g KCl was added, filtered, and the filter cake was recrystallized in a solution of pH 2 in hydrochloric acid to give P₂W₁₅Mo₃。P₂W₁₃Mo₅By the same synthetic method, adding Na₂MoO₄It was 5.6 g. P₂W₁₅V₃The same synthesis method is adopted, and the vanadium source is NaVO₃。

Example 6

Preparation of a polyoxometalate of Dawson type with W atom substituted by two heteroatoms and number of substitutions higher than 3: taking P2W15Mo2V as an example, 47g P is added into 250ml of water₂W₁₅Mo₂，20ml 0.5mol/L NaVO₃Solution, 40ml of 1 mol/L HCl, followed by addition of 25g of KCl, filtration and drying in air, gives P₂W₁₅Mo₂V。P₂W₁₅MoV₂The same procedure was used.

Example 7

Preparation of the supported catalyst: the catalyst is prepared by an impregnation method by taking phosphotungstic acid (5%)/P2W 17 (10%) which is a composite catalyst loaded with 5 wt% of phosphotungstic acid and 10 wt% of P2W 17. 1g of hydrotalcite is immersed into a mixed aqueous solution containing 5g/L of phosphotungstic acid and 10g/L P2W17, the pH value is adjusted to 5.5, the mixed aqueous solution is stirred for 24 hours at the temperature of 30 ℃, the mixed aqueous solution is filtered, dried and calcined for 6 hours in a nitrogen atmosphere, the loading capacity of the phosphotungstic acid is 5 percent, the loading capacity of the P2W17 is 10 percent, and the loading capacity is marked as phosphotungstic acid (5%)/P2W 17(10 percent). The preparation method of other supported catalysts is the same, and only the feeding amount of polyoxometallate is changed.

Examples 8 to 18

Weighing 500mg of sawdust and 1g of catalyst, mixing in a high-pressure reaction kettle, adding 20ml of methanol, introducing oxygen, raising the temperature to 120 ℃ at an initial pressure of 1.0MPa and a rotation speed of 1500r/min, and keeping the temperature for 6 hours. After the reaction was completed, it was cooled to room temperature, the pressure was released, centrifuged, and the liquid phase product was collected, and the results are shown in Table 1.

Example 19

Weighing 500mg of sawdust and 1g of phosphotungstic acid (5%)/P2W 17 (10%) catalyst, mixing in a high-pressure reaction kettle, adding 20ml of methanol, introducing oxygen, raising the temperature to 100 ℃ at an initial pressure of 1.0MPa and a rotation speed of 1500r/min, and keeping the temperature for 6 hours. After the reaction was completed, it was cooled to room temperature, the pressure was released, centrifuged, and the liquid phase product was collected, and the results are shown in Table 1.

Example 20

Weighing 500mg of sawdust and 1g of phosphotungstic acid (5%)/P2W 17 (10%) catalyst, mixing in a high-pressure reaction kettle, adding 20ml of methanol, introducing oxygen, raising the temperature to 120 ℃ at an initial pressure of 2.0MPa and a rotation speed of 1500r/min, and keeping the temperature for 6 hours. After the reaction was completed, it was cooled to room temperature, the pressure was released, centrifuged, and the liquid phase product was collected, and the results are shown in Table 1.

Example 21

Weighing 500mg of sawdust and 1g of phosphotungstic acid (5%)/P2W 17 (10%) catalyst, mixing in a high-pressure reaction kettle, adding 20ml of methanol/ethanol (4/1) (ml/ml) mixed solvent, introducing oxygen, raising the initial pressure to 1.0MPa, rotating at 1500r/min, and keeping the temperature at 120 ℃ for 6 hours. After the reaction was completed, it was cooled to room temperature, the pressure was released, centrifuged, and the liquid phase product was collected, and the results are shown in Table 1.

Example 22

Weighing 500mg of sawdust and 500mg of phosphotungstic acid (5%)/P2W 17 (10%) catalyst, mixing in a high-pressure reaction kettle, adding 20ml of methanol, introducing oxygen, raising the temperature to 120 ℃ at an initial pressure of 1.0MPa and a rotation speed of 1500r/min, and keeping the temperature for 6 hours. After the reaction was completed, it was cooled to room temperature, the pressure was released, centrifuged, and the liquid phase product was collected, and the results are shown in Table 1.

Example 23

Weighing 500mg of sawdust and 1g of phosphotungstic acid (5%)/P2W 17 (10%) catalyst, mixing in a high-pressure reaction kettle, adding 20ml of methanol, introducing oxygen, raising the temperature to 120 ℃ at an initial pressure of 1.0MPa and a rotation speed of 1000r/min, and keeping the temperature for 6 hours. After the reaction was completed, it was cooled to room temperature, the pressure was released, centrifuged, and the liquid phase product was collected, and the results are shown in Table 1.

TABLE 1 statistical table of the catalytic oxidation degradation reaction results of the composite catalyst under different conditions

Table 1 examples 8 to 23 reaction liquid phase products are mainly aromatic aldehyde and ketone compounds, and the preferable results are determined according to the system liquid phase yield: the catalyst is phosphotungstic acid (5%)/P2W 17 (10%), the solvent is methanol, the reaction temperature is 120 ℃, the reaction time is 6h, the catalyst is oxygen, the pressure is 1.0MPa, the catalyst concentration is 0.05g/ml, and the stirring speed is 1500 r/min.

The above description is only a preferred embodiment of the present invention, and these embodiments are based on different implementations of the overall concept of the present invention, and the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention should be covered by the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. a method for polyoxometalate catalytic oxidation degradation sawdust, is characterized in that, comprises the following steps:

(1) Mix the wood chips and the reaction solvent in a proportion of 300~700 mg: 20 ml and place them in the autoclave, and add the double polyoxometalate/hydrotalcite composite catalyst; (2) Seal the autoclave and replace the air in the autoclave After the reaction, the oxidizing agent was charged, the stirring was started, and then the reaction temperature was 100-180 ºC for oxidative degradation for 2-10 h; (3) After the reaction was completed, it was cooled to room temperature and obtained by centrifuging the residue in the kettle after the reaction. oxidative degradation products;

Wherein the double polyoxometalate/hydrotalcite composite catalyst includes two catalytic centers, and one catalytic active center is selected from Keggin-type polyoxometalate phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, and silico-molybdic acid. One or more, the two catalytic active centers are selected from Dawson type polyoxometalate P ₂ W ₁₈ , Dawson type Dawson type P ₂ W ₁₇ , heteroatom substituted Dawson type P ₂ W ₁₇ Mo, P ₂ W ₁₅ Mo _3. _One _or _more _of _P2W13Mo5 _, _P2W17V _, _P2W15V3 _, _P2W13V5 _, _P2W15Mo2V _, _P2W15MoV2 _{_} _{_} .

2. The method according to claim 1, wherein the solvent is an alcohol or an alcohol-containing mixed organic solvent.

3. The method according to claim 1, wherein the mass fraction of the catalytically active center one is 2 to 10%, and the mass fraction of the catalytically active center two is 5 to 20%.

The method according to claim 1, wherein the catalyst carrier is magnesium aluminum hydrotalcite [Mg ₆ Al ₂ (OH) ₁₆ ](CO ₃ ), and the composite catalyst is prepared by an impregnation method.

5 . The method according to claim 1 , wherein the oxidative degradation products comprise aldehyde and ketone small molecular compounds. 6 .

6. method according to claim 1, is characterized in that, the concentration of double polyoxometalate/hydrotalcite composite catalyst is 0.02～0.5 g/ml in the blended solution.

7. The method of claim 1, wherein the oxidant is oxygen.

8 . The method according to claim 7 , wherein the initial pressure of the oxidant O ₂ in the oxidative degradation reaction is 0.2 to 2.5 Mpa. 9 .

9. method according to claim 1, is characterized in that, the rotating speed of described stirring is 500～1500 r/min.